"Our customers are very excited about the freedom and amazing sound quality of iTunes Plus," Apple chief executive Steve Jobs said in a release. "We expect more than half of the songs on iTunes will be offered in iTunes Plus versions by the end of this year."

Jobs denounced digital rights management software in February in an open letter calling on the music recording industry to abandon the practice of insisting it be incorporated into digital music sold online.

Major recording studios fired back that the safeguard is needed to prevent pirates from making myriad unauthorised copies and denying owners their due payments for music. Cupertino, California-based Apple and EMI, based in Britain, formed an alliance in April to sell DRM-free music.

"This is a tremendous milestone for digital music," EMI Group chief executive Eric Nicoli said of the new iTunes offering. "Consumers are going to love listening to higher quality iTunes Plus tracks from their favourite EMI artists with no usage restrictions."

The removal of DRM software means that for the first time music bought at iTunes can be played on rival MP3 players, including Microsoft's Zune, and not just on Apple's iPod.